Using a radioimmunoassay and/or an enzyme-linked immunoassay and purified bacterial carbohydrate antigens, we will study a large collection of sera from cases of neonatal group B streptococcal (GBS) spesis, maternal and infant carriers of GBS and carefully matched controls. We will attempt to confirm an inverse relationship between type-specific antibody and the occurrence of GBS sepsis and to define more clearly a protective level of antibody. We will determine the prevalence and levels of type-specific antibody to all serotypes in young adults of reproductive age in relation to age, parity, ethnic group, geographical locale and carriage of GBS. Using serial bleedings and prospective bacteriological data, we will study the antibody response to streptococcal carriage, searching for evidence of IgM antibody and a primary immune response. We will examine breask milk (and serum) from lactating mothers for specific antibody of different immunoglobulin classes (IgG, M and A) and for secretory IgA antibody. If specific secretory IgA antibody in breask milk is prevalent, we propose two prospective studies: one to study the origin of breask milk IgA antibody in genital and/or intestinal carriage of GBS during pregnancy and the other to evaluate the protective effect of breast milk antibody on neonatal acquisitions of GBS in the hospital nursery. We also hope to study specific antibody of IgG subclasses, focusing on IgG-2 in the serum of septic infants and their controls and on pregnant patients of different ethnic groups. Using the same methodology as for antibody to type-specific carbohydrates, we will study the human antibody response to the group B antigen, especially in relationship to carriage during pregnancy. These studies are intended to provide a better understanding of the human response to GBS infection and carriage and the protective significance of antibody and to suggest possible means of preventing an important neonatal infection.